1. Field of the Invention
The present invention relates to a photo film cassette, and more specifically to a photo film cassette having a spool on which photo film can be secured easily, a method of loading the film and an apparatus for such loading.
2. Description of the Related Art
Photo film of the 135 type, contained in a cassette, is the most popular type marketed currently. The 135 photo film cassette has a cassette shell constituted of a cylindrical body and two end caps. The cylindrical body is formed of a thin metal plate, with the caps fitted thereon. The cassette has a spool on which photo film is wound in a form of a roll and which is contained in the cassette shell. To assemble this photo film cassette, several methods are known. According to the method disclosed in U.S. Pat. No. 4,614,019 (corresponding to JP-B 2-691) for example, the photo film is first wound on the spool. The cassette is then assembled while covering the photo film within the cassette shell in a darkroom.
U.S. Pat. No. 3,910,516 (corresponding to JP-A 49-107732) and JP-A 52-77723 also suggest a photo film cassette producing method. In this method, a spool is incorporated into an empty cassette in an illuminated room. A tongue-like guide plate is then inserted into a photo film passage port formed in the cassette. Then, in a darkroom, a trailer of photo film is inserted into the cassette while being guided along the guide plate. The trailer is retained on the spool fixedly. The spool is finally rotated to wind the photo film up into the cassette.
It is also suggested by U.S. Pat. Nos. 4,834,306 and 4,846,418 and a commonly assigned European patent application published as EP-A2 0 406 815 (corresponding to JP-A 3-37645) to construct a photo film cassette in which a cassette shell is constituted of parts formed from resin, and rotation of a spool causes a leader of the photo film to exit to the outside of the cassette. Such a leader-advancing cassette is different from photo film cassettes conventionally in use because the leader of the photo film is fully contained within the cassette even before exposure and after exposure. The cassette has advantages in that the photo film is reliably protected from accidental exposure to ambient light. Also, the lack of external protrusion of the leader facilitates handling of the cassette.
The assignee of the present application has proposed a photo film cassette in which a spool has a slot for receiving a trailer of the photo film. In the slot, retaining hooks are formed. Holes formed in the trailer are fitted on the hooks. Also, slip-preventive ridges are formed in opposition to the hooks and at positions beside the hooks. The ridges contact with the trailer, press the trailer against an opposite wall of the slot, and retain the trailer inside the slot in cooperation with the hooks. The trailer is thus prevented from disengagement from the slot, and is reliably secured to the spool.
However, it is difficult to insert the trailer into the above-described spool, mainly due to the arrangement of the hooks and the ridges. The tops of the hooks extend beyond the opposite tops of the ridges, so that the trailer must be bent or curved forcibly before the trailer can be fully inserted into the slot between the hooks and ridges. Even when the trailer is safely inserted, excessive force for the insertion is required. In production of this cassette, the above-described tongue-like guide plate as proposed in U.S. Pat. No. 3,910,516 and JP-A 52-77723 could be used for assistance in the insertion of the trailer into the cassette. However, the guide plate might also be bent or curved inside the slot during guiding the trailer.
There is an alternative proposal as suggested in a commonly assigned U.S. Pat. No. 5,360,183 (corresponding to JP-A-4-122925). A spool disclosed therein has a slot for receiving a trailer. In the slot, retaining hooks and slip-preventive ridges are formed. The hooks are retractable from inside the slot. In the course of advancing the trailer into the slot, the hooks are retracted. When the holes come to the hooks, the hooks are resiliently recovered into the slot, are fitted into the holes, and retain the trailer. This alternative has problems in that the trailer cannot have a stable position inside the slot, and has low reliability in successful engagement with the hooks. Even after the engagement, the hooks can be moved by shock or vibration of the cassette, and the trailer is accidently disengaged from the hooks.